Development Of Flue Gas Purification Device Based On PLC Control

Thermal coal-fired units emit flue gas,which contains a large amount of dust,nitrogen oxides,sulfur dioxide and other harmful gases and particulate matter,during the process of completing power generation.This paper focuses on the problems of uneven flue gas flow field in the flue gas denitration unit of a coal-fired power plant,which needs to achieve ultra-low emission of gaseous pollutants,and combines numerical simulation methods to optimize the rectification structure and enhance the mixing effect of flue gas and ammonia gas.Based on the characteristics of denitration system,such as large delay and strong cou-pling,a fuzzy control method is proposed to optimize the control accuracy of ammonia injection volume and ensure that the NO_X concentration at the outlet meets the emission standard.At the same time,the upper computer and touch screen are used to provide a visual monitoring platform for engineers to complete the tasks of data acquisition and online re-al-time monitoring.To sum up,it is necessary to develop a reasonable structure and high performance automatic device for flue gas denitration.The main research contents of this paper are as follows:(1)The selection of catalytic reduction(SCR)technology as the denitrification scheme for coal-fired power plants is determined,and the basic chemical principles of SCR deni-trification,the basic composition and operating principles of the device are introduced and analyzed.Aiming at the unreasonable rectification structures of the denitrification device in the power plant,the numerical simulation analysis and calculation method is used to pro-pose the use of angle steel grids instead of the porous plate equalizer in the original scheme,while four different operating conditions are designed and their velocity distribution dia-grams,ammonia concentration distribution diagrams and pressure drops in each part of the system are compared horizontally.(2)Through the analysis of the traditional SCR denitration control strategy,the control of ammonia injection quantity in denitration system is determined as the key research ob-ject.As SCR denitration system is a control object with large delay,strong coupling and nonlinear,the conventional cascade PID control has some problems such as excessive ammonia spraying.Fuzzy control algorithm is introduced to optimize the ammonia spray-ing quantity.The simulation results show that fuzzy PID control has strong advantages in adjusting time and stability.(3)The control system mainly adopts PLC as the control core and Siemens S7-300 as the controller.The S7-300 communicates with the upper computer through Ethernet.Design the hardware of the control system,draw the hardware wiring diagram of the system,list the I/O table of the control system,complete the circuit diagram of the power cabinet and lightning protection grounding design.(4)Write PLC ladder diagram program according to the control logic of each part of SCR flue gas denitration device,and apply fuzzy control to PLC.Through Win CC config-uration software to complete the design of the upper computer and touch screen,complete the temperature,liquid level,pressure,flue gas containing NOx amount monitoring,im-prove the automation of the control system.